Flat panel screens, in particular plasma display panels (PDPs), enable color pictures with high definition, large screen diagonals, and have a compact structure. A plasma screen comprises a sealed gas-filled glass cell with grid-like arranged electrodes. By applying an electric voltage, a gas discharge is caused which mainly generates light in the vacuum ultraviolet range (“VUV”). Fluorescence transforms this VUV light into visible light and the front plate of the glass cell emits this visible light to the viewer.
When compared to LCD-type large area displays or televisions, PDPs suffer from poor contrast in bright viewing conditions, because ambient light is reflected by the emission cells of the PDP and washes out the blacks in an image. Since LCD and plasma TV's are now comparable in selling price, contrast performance is becoming a deciding factor in the purchase of a flat panel TV. Plasma TV manufacturers are searching for a simple and low-cost method of improving the contrast, in particular, daytime or high ambient light contrast, of their displays, that does not degrade other PDP performance characteristics, such as resolution and on-axis luminance or brightness.
Several solutions to this problem have been proposed involving various louvre structures. In general, there is a tradeoff between increasing contrast and decreasing transmission (i.e., increasing contrast with a filter decreases the brightness). In practice, the best systems can achieve 70% transmission.
One prior-art device for improving the black-level of a PDP is presented in FIG. 1. In this setup, PDP pixels 10A and 10B are situated behind a glass layer 12 of the display panel onto which is installed a film 15 for ambient light absorption. The ambient light absorption film 15 has a substrate 18 onto which is installed a series of black light-absorbing strips 14 between which are transparent apertures 16. The front face 20 of the ambient light absorption film 15 is transparent, but may be textured to reduce ambient light glare.
In operation, ambient light ray 30 that originates from a light source in the vicinity of the PDP, typically from an overhead room light, is incident on the front face 20 and refracts into the substrate 18 before striking a black stripe 14 at location 40 where it is absorbed. In this way ambient light is absorbed and prevented from reaching the highly reflective pixels 10A and 10B. However, light rays such as ray 32 refract through the front surface 20 into the substrate 18, but then miss the black stripes 14 and pass through an aperture 16 at position 42 unattenuated. This ray then passes through the glass layer 12 and is then incident on a PDP pixel 10A, at location 44 whereupon it is backscattered into a full hemisphere. Some of the backscattered light, such as ray 36, will be incident on a black stripe and be absorbed, such as at location 48. However other rays, such as ray 34, will pass through an aperture at position 46 between the black stripes and will exit the PDP system. These rays can be easily seen by the TV viewer, and degrade the viewing performance of the PDP by making the black colors appear gray, and by making the saturated colors appear dingy and pale.
The ambient light absorption film 15 also impacts the brightness of the PDP because a large portion of the light rays emitted by the pixels are absorbed by the black stripes. For example, light ray 62 emitted from pixel 10B at location 52 passes through the glass 12 and immediately strikes the backside of a black stripe at location 54 and is absorbed. On the other hand, light ray 64 emitted from pixel 10B at location 50 is able to pass through an aperture of the ambient light absorption film 15 at location 56 unattenuated.
To obtain maximum brightness then, the ratio of the width of the apertures 16 to the pitch of the black stripes needs to be maximized. But this is at odds with how black-level performance is maximized, and typically a trade-off between transmittance and ambient light absorption must be made at the light absorption film 15. Because of this compromise generally both the light transmission of the film and the ambient light absorption characteristics are deemed to be inferior to the performance of the LCD-type displays.
Consequently there is a genuine need for an ambient light absorption film that has high display light transmission and also high ambient light absorption that is easily constructed. The present invention is directed to overcoming these and other deficiencies in the art.